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diff --git a/files/zh-cn/web/javascript/reference/global_objects/string/fromcodepoint/index.html b/files/zh-cn/web/javascript/reference/global_objects/string/fromcodepoint/index.html new file mode 100644 index 0000000000..786125e340 --- /dev/null +++ b/files/zh-cn/web/javascript/reference/global_objects/string/fromcodepoint/index.html @@ -0,0 +1,144 @@ +--- +title: String.fromCodePoint() +slug: Web/JavaScript/Reference/Global_Objects/String/fromCodePoint +translation_of: Web/JavaScript/Reference/Global_Objects/String/fromCodePoint +--- +<div>{{JSRef}}</div> + +<p><strong><code>String.fromCodePoint()</code> 静态方法返回使用指定的代码点序列创建的字符串。</strong></p> + +<div>{{EmbedInteractiveExample("pages/js/string-fromcodepoint.html")}}</div> + + + +<h2 id="语法">语法</h2> + +<pre class="syntaxbox"><code>String.fromCodePoint(<var>num1</var>[, ...[, <var>numN</var>]])</code></pre> + +<h3 id="参数">参数</h3> + +<dl> + <dt><code>num1, ..., num<em>N</em></code></dt> + <dd>一串 Unicode 编码位置,即“代码点”。</dd> + <dt> + <h3 id="返回值">返回值</h3> + + <p>使用指定的 Unicode 编码位置创建的字符串。</p> + </dt> +</dl> + +<h3 id="异常">异常</h3> + +<dl> + <dt>{{jsxref("RangeError")}}</dt> + <dd>如果传入无效的 Unicode 编码,将会抛出一个{{jsxref("RangeError")}} (例如: "RangeError: NaN is not a valid code point")。</dd> +</dl> + +<h2 id="说明">说明</h2> + +<p>该方法返回一个字符串,而不是一个 {{jsxref("String")}} 对象。</p> + +<p>因为 <code>fromCodePoint()</code> 是 {{jsxref("String")}} 的一个静态方法,所以只能通过 <code>String.fromCodePoint()</code> 这样的方式来使用,不能在你创建的 {{jsxref("String")}} 对象实例上直接调用。</p> + +<h2 id="例子">例子</h2> + +<h3 id="使用_fromCodePoint()">使用 <code>fromCodePoint()</code></h3> + +<pre class="brush: js">String.fromCodePoint(42); // "*" +String.fromCodePoint(65, 90); // "AZ" +String.fromCodePoint(0x404); // "\u0404" +String.fromCodePoint(0x2F804); // "\uD87E\uDC04" +String.fromCodePoint(194564); // "\uD87E\uDC04" +String.fromCodePoint(0x1D306, 0x61, 0x1D307) // "\uD834\uDF06a\uD834\uDF07" + +String.fromCodePoint('_'); // RangeError +String.fromCodePoint(Infinity); // RangeError +String.fromCodePoint(-1); // RangeError +String.fromCodePoint(3.14); // RangeError +String.fromCodePoint(3e-2); // RangeError +String.fromCodePoint(NaN); // RangeError +</pre> + +<pre class="brush: js">// String.fromCharCode() 方法不能单独获取在高代码点位上的字符 +// 另一方面,下列的示例中,可以返回 4 字节,也可以返回 2 字节的字符 +// (也就是说,它可以返回单独的字符,使用长度 2 代替 1!) +console.log(String.fromCodePoint(0x2F804)); // or 194564 in decimal +</pre> + +<h2 id="Polyfill">Polyfill</h2> + +<p><code>String.fromCodePoint</code> 方法是 ECMAScript2015(ES6)新增加的特性,所以一些老的浏览器可能还不支持。可以通过使用下面的 polyfill 代码来保证浏览器的支持:</p> + +<pre class="brush: js">if (!String.fromCodePoint) (function(stringFromCharCode) { + var fromCodePoint = function(_) { + var codeUnits = [], codeLen = 0, result = ""; + for (var index=0, len = arguments.length; index !== len; ++index) { + var codePoint = +arguments[index]; + // correctly handles all cases including `NaN`, `-Infinity`, `+Infinity` + // The surrounding `!(...)` is required to correctly handle `NaN` cases + // The (codePoint>>>0) === codePoint clause handles decimals and negatives + if (!(codePoint < 0x10FFFF && (codePoint>>>0) === codePoint)) + throw RangeError("Invalid code point: " + codePoint); + if (codePoint <= 0xFFFF) { // BMP code point + codeLen = codeUnits.push(codePoint); + } else { // Astral code point; split in surrogate halves + // https://mathiasbynens.be/notes/javascript-encoding#surrogate-formulae + codePoint -= 0x10000; + codeLen = codeUnits.push( + (codePoint >> 10) + 0xD800, // highSurrogate + (codePoint % 0x400) + 0xDC00 // lowSurrogate + ); + } + if (codeLen >= 0x3fff) { + result += stringFromCharCode.apply(null, codeUnits); + codeUnits.length = 0; + } + } + return result + stringFromCharCode.apply(null, codeUnits); + }; + try { // IE 8 only supports `Object.defineProperty` on DOM elements + Object.defineProperty(String, "fromCodePoint", { + "value": fromCodePoint, "configurable": true, "writable": true + }); + } catch(e) { + String.fromCodePoint = fromCodePoint; + } +}(String.fromCharCode)); +</pre> + +<h2 id="规范">规范</h2> + +<table class="standard-table"> + <tbody> + <tr> + <th scope="col">规范</th> + <th scope="col">状态</th> + <th scope="col">备注</th> + </tr> + <tr> + <td>{{SpecName('ES2015', '#sec-string.fromcodepoint', 'String.fromCodePoint')}}</td> + <td>{{Spec2('ES2015')}}</td> + <td>Initial definition.</td> + </tr> + <tr> + <td>{{SpecName('ESDraft', '#sec-string.fromcodepoint', 'String.fromCodePoint')}}</td> + <td>{{Spec2('ESDraft')}}</td> + <td> </td> + </tr> + </tbody> +</table> + +<h2 id="浏览器兼容性">浏览器兼容性</h2> + +<p class="hidden">The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out <a href="https://github.com/mdn/browser-compat-data">https://github.com/mdn/browser-compat-data</a> and send us a pull request.</p> + +<p>{{Compat("javascript.builtins.String.fromCodePoint")}}</p> + +<h2 id="参见">参见</h2> + +<ul> + <li>{{jsxref("String.fromCharCode()")}}</li> + <li>{{jsxref("String.prototype.charAt()")}}</li> + <li>{{jsxref("String.prototype.codePointAt()")}}</li> + <li>{{jsxref("String.prototype.charCodeAt()")}}</li> +</ul> |